Ashton Kutcher: Cameron Diaz 'Doing Well'

After his costar lost her father last week, Ashton Kutcher ably represented Cameron Diaz at London’s world premiere of their new movie together, What Happens in Vegas.

“She is doing well … as well as you can do,” Kutcher said on the red carpet Tuesday night – exactly a week after Emilio Diaz’s sudden death from pneumonia in Southern California. The actress’s father was 58.

“It is really unfortunate,” said Kutcher, 30, explaining that Cameron, 35, was back home, “helping out with services and stuff.”

Personally, Kutcher said of the actress, “I am desperately missing her tonight. We made a present, and it’s like I have to open it alone – and you want to open the present you want to share.”

Kutcher, who plainly adored working with Diaz, also expressed concern for her.

“I can’t imagine losing my dad,” he said. “That would be … a pretty tragic deal. But I think she’s doing good, and you know what? She’ll be happy that’s she’s making people happy, and she’s great for the movie.”

Marital Comedy

The comedy, which also stars Queen Latifah as a marriage counselor, has the two as unlikely newlyweds bound together – and yet torn apart – by a $3 million jackpot. It opens May 9 in the U.S.

The film’s director, Tom Vaughan, told PEOPLE he lamented Diaz’s absence from the premiere. “It is a very sad personal tragedy. She really wanted to be here,” he said, further noting, “She has got a very good group of people around her – friends.”